The invention relates to a vehicle occupant protection system comprising a gas bag, in particular a side gas bag.
Especially in vehicle occupant protection systems with side window gas bags, frequently tensioning straps are used to fix the gas bag in position in a vehicle. In the case of side window gas bags which in the unfolded state extend from the A- to the C-column of the vehicle and which in the folded state are arranged in the region of the vehicle roof, the problem exists that owing to the curvature of the roof frame, the length of the gas bag in the folded state is greater than the desired length in the inflated state. It is known to achieve an anchoring of the gas bag via a shortening of the length of the tensioning straps which are used for fixing the gas bag in position. This can take place for example by a spring mechanism arranged in the region of the A-column or C-column or a piston/cylinder device. Such devices for tensioning the tensioning strap are expensive to produce and are complicated to install on the vehicle.
The invention addresses the problem of providing a vehicle occupant protection device which offers a simple and favorably-priced anchoring of the gas bag.
This is achieved in a vehicle occupant protection system comprising a gas bag which has at least one inflatable chamber including a wall. The protection system further comprises a tensioning strap which fixes the gas bag in position in an inflated state. The tensioning strap is fully looped around the wall of the inflatable chamber and fastened to the wall and to the vehicle in such a manner that inflating the chamber causes a displacement of the tensioning strap and a tightening of the tensioning strap. The looping around the chamber, with the tensioning strap going completely around the chamber, allows for a particularly good use of an increase in volume of the chamber. During filling of the gas bag, the increase in volume of the chamber which has the tensioning strap looped around it provides for those sections of the tensioning strap which are located in direct vicinity to the chamber, to experience a force oriented towards the chamber and to be pulled into the section of the tensioning strap which loops around the chamber. These sections of the tensioning strap are regarded as being located in direct vicinity to the chamber which before or during the filling of the gas bag adjoin directly to the section looping around the chamber. Thus, an effective xe2x80x9cshorteningxe2x80x9d of the tensioning strap and with this an anchoring of the gas bag can be achieved. As in the way the gas itself is used for tightening the tensioning strap, a further mechanism can be dispensed with, which reduces costs and effort.
The tensioning strap is displaceable with respect to the wall of the chamber, so that during filling of the chamber the adjoining sections of the tensioning strap can be xe2x80x9cpulled intoxe2x80x9d the section looping around the chamber.
In order to not hinder the tensioning strap from moving relative to the chamber, it is favorable if the tensioning strap loops around the chamber in a spiral fashion.
The distance, contributing to the anchoring, by which the tensioning strap is shortened through the increase in volume of the chamber which has the strap looped around it, can be increased in that the tensioning strap is laid around the chamber in at least two loops.
Preferably the gas bag has several chambers, and the chamber which has the tensioning strap looped around it, hereinafter named the anchoring chamber, serves principally for tightening the tensioning strap, whilst the other chambers are provided for restraining purposes.
Preferably the anchoring chamber has a higher internal pressure and, where appropriate, a wall which is more gas-tight than the other chambers. As no consideration has to be given to the restraining characteristics of the anchoring chamber, it can be optimized to its anchoring purpose by adjusting the pressure and the gas-tightness.
For this purpose, preferably a gas distributor is provided via which gas, which is generated by a gas generator in the case of restraint, is directed into the individual chambers, the gas distributor being designed such that in the inflated state a different pressure can prevail in the individual chambers. By means of such a known gas distributor, which may also be embodied as a gas lance, the higher internal pressure of the anchoring chamber can be realized, as compared with the other restraint chambers.
In a preferred embodiment of the invention, the gas bag is a side window gas bag. The tensioning strap preferably runs substantially parallel to the lower edge of the side windows of the vehicle. It is particularly advantageous if the side window gas bag has three inflatable chambers arranged adjacent each other, the tensioning strap being looped around the central chamber. The anchoring effect occurs particularly clearly if the chambers of the gas bag are connected with each other at the lower edge only by means of the tensioning strap. As seen in a projection onto a plane parallel to the side windows of the vehicle, the section of the tensioning strap looping around the chamber runs in this embodiment preferably parallel to a lower edge of the side windows of the vehicle, so that the tensioning strap extends along an imaginary straight line between fastening points on the vehicle, whereby a uniform anchoring of the lower edge of the gas bag can be achieved.
Preferably the ends of the tensioning strap are fastened to the walls of the two outer chambers. The walls of the outer chambers can be fastened in addition by means of further tensioning straps to vehicle-fixed parts. In this way, the overall length of the tensioning strap can be kept as short as possible, and a correct unfolding of the gas bag can be achieved.
Another alternative makes provision that the ends of the tensioning strap are connected directly to vehicle-fixed parts. In this case, only a single long tensioning strap can be provided which loops around the central chamber and runs for example through eyes on the outer chambers and can be fastened to the A- and C-column of the vehicle. Thereby, sewing the tensioning strap to the individual walls of the chambers can be avoided.
In a further preferred embodiment of the invention a deflection member is provided which is connected to a vehicle part such as the A- or the C-column and which is arranged in the run of the tensioning strap between the chamber which has the strap looped around it and a fastening point of the tensioning strap on the gas bag. That is, the tensioning strap can run from a fastening point on the gas bag through the deflection member to the chamber. A particularly suitable variant makes provision that the tensioning strap runs from the chamber which has the strap looped around it, to a second deflection member and from there to a second fastening point located at the other end of the gas bag. In this way the gas bag can be anchored by means of only one tensioning strap.
Preferably, the chamber which has the tensioning strap looped around it extends only in the region of the roof frame, i.e. it does not reach the lower edge of the side windows. As this chamber mainly serves for anchoring the gas bag and not so much for restraining, gas bag volume can be saved in this way. An additional advantage of this arrangement lies in the fact that, with the above-mentioned three-chamber design of the gas bag, a run of the tensioning strap may be chosen in which the tensioning strap extends obliquely along the restraint chambers and thus the latter can be fixed in position when the side windows are destroyed, for example.